Catalysts for Organic Chemistry 2017 by Acros

More catalogs by Acros | Catalysts for Organic Chemistry 2017 | 16 pages | 2017-07-19


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Catalog Catalysts for Organic Chemistry 2017

zinc chloride cesium thf c 37832 bf4 br5 arbr hauck benzyl acetate silane coupling agent sp2 chloroform n nonane nonane malm potassium iodide tetra magnesium chloride sodium iodide fu wang 1999 buell m 2 lithium bromide activated alumina vinyl chloride jensen stereo myer catalogue sp 995 1980 suzuki 96 trans am vch 10 verlag free 1975 am general

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most of these coupling reactions have a similar catalytical cycle the heck-reaction differs slightly 2 the following pages give an overview over the most common carbon-carbon and carbon-heteroatom coupling reactions the catalysts and the substrates offered by acros organics 4 metal catalysts 2 ch.elschenbroich a.salzer organometallchemie b.g.teubner stuttgart

sonogashira-reaction 1 precious-metal catalysts from acros organics for coupling reactions in organic synthesis ii the sonogashira-reaction and the closely related stephens-castro reaction2 consists of the palladium-catalysed coupling of copper-acetylides and arylhalogenides to yield alkynylarenes3 scheme 1 this reaction is one of the most important reactions to produce alkenyl and aryl-acetylenes4 which have recently got a lot of attention as endiyn-antibiotics5,6 scheme 2 the use of silylated acetylene avoids the coupling at both positions but if required the silyl-protecting group can be removed in-situ to enable the second coupling reaction i.e for the synthesis of un-symmetric bis-arylethynes7 scheme 3 the sonogashira-reaction has a broad scope tolerating several functional groups it can be performed with ammonia as base in aqueous solution8 and even works with palladium on carbon as catalyst9 instead of homogeneous palladium catalysts recent improvements of the reaction are

suzuki-reaction 1 precious-metal catalysts from acros organics for coupling reactions in organic synthesis iii amongst the growing number of palladium-catalysed c-c-coupling reactions the suzuki-miyaura-reaction2 plays a leading role in this reaction an aryl-halogenide is coupled with a aryl or vinyl-boronic acid or boronic-ester to unsymmetric biaryles scheme 1 major advantages of the suzuki-reaction are • the stability of the boron-reagents3 • the easy access to a broad variety boronic-acids through different synthetic pathways scheme 24,5 • the tolerance for different functional groups • the simple experimental conditions the suzuki-miyaura-reaction was also extended to b-alkyl compounds6 the effects of the catalysts ligands solvents and substrates have been investigated1,7 the catalyst tetrakistriphenylphosphinepalladium is most common but also other homogeneous catalysts as well as immobilised or heterogeneous8 palladium-compounds have been used reagents

stille-reaction 1,2 precious-metal catalysts from acros organics for coupling reactions in organic synthesis iv the stille-coupling is the palladium-catalyzed reaction between organo-stannanes and organic halides3 typically the stannane is sp2 or sp-hybridised aryl alkenyl alkinyl but also alkyl allyl and benzyl-stannanes and others have been used the reactivity follows the order alkynyl alkenyl aryl allyl benzyl>alkyl the halides are usually bromides or iodides and also triflates arylchlorides are less reactive but can be used in good yields with a catalyst-system pd2dba3 csf and tri-tert.butylphosphine the organic halides may be aryl vinyl acyl-11,6,7 substituted2 in the presence of carbon monoxide the coupling happens with insertion of co the stille-coupling can be influenced by additives like copper 8 and silver9-salts and lithium chloride10 the pathway of the reaction has been studied11 the catalytic cycle is similar to other palladium2 catalyzed cross-coupling reactions

hiyama-coupling 1,2 precious-metal catalysts from acros organics for coupling reactions in organic synthesis v the hiyama-coupling is the palladium-catalysed reaction between aryland alkenyl halogenides or -triflates with organo-silanes the reaction rate is increased by activating the silane with fluoride and by using chloro and fluorosilanes instead of trimethylsilanes3 also microwaves have been used to accelerate the reaction rate4 the hiyama-coupling is comparable with the stille-coupling with the advantage of avoiding toxic tin-compounds in the reaction recently the use of siloxanes and of silacyclobutanes6 in the hiyama-coupling has been reported the reaction tolerates several functional groups and also different aromatic or vinylic systems can be transferred7 reagents for the hiyama coupling from acros organics vinyltrimethylsilane 97 20033 phenyltrimethoxysilane 37064 tetravinylsilane 97 31373 dichloromethylphenylsilane 98 14738 triethylvinylsilane 97 31377

kumada-coupling 1,2,3 precious-metal catalysts from acros organics for coupling reactions in organic synthesis vi the kumada-coupling is the nickel4 or palladium-catalysed reaction between aryl and vinylhalogenides or –triflates and aryl alkenyl or alkyl grignard-reagents5,6 also heteroaryl-7 and alkyl8-halides can be coupled with grignard reagents the reactivity of the halogenides follows the order i br cl when palladium is used as catalyst whereas with certain nickel-catalysts the order is cl i br5 z alkenyl-grignards couple non-stereospecific with nickel catalysts2 but the reaction is stereospecific “retention of configuration” with palladium-catalysts9 the phosphine-ligand has also a strong influence on the yield bidentate ligands generally bear a higher activity than monodentate phosphines bisdiphenylphosphinopropane ao 31005 is optimal for most reactions2 the kumada-coupling is somewhat limited because of the incompatibility of grignard-reagents with

tsuji-trost-reaction 1,2 precious-metal catalysts from acros organics for coupling reactions in organic synthesis viii the tsuji-trost reaction is the widely used palladium catalysed substitution of allylic or propargylic3-compounds with carbon nucleophiles like enolates or other stabilised carbanions4 such as α-sulfonyl αnitro or α-cyanocarbanions4 the reaction proceeds through allyl-palladium intermediates5 in the first example tsuji1 reported the reaction of allylpalladium chloride dimer ao 20683 with ethylmalonate and ethylacetoacetate a broad variety of allylic compounds can been used4 although allyl-acetates are most common the chemo regio and stereoselectivity6 of the tsuji-trost-reaction have been intensively studied7 the enantioselectivity with chiral phosphine-ligands8,9,10,11,12 was also featured by numerous extensive studies13 the allylic substitution can also be catalysed with other metal-complexes like [ircodcl]14 ao 36938 and especially some tungsten and

cyanation of aromatic halides precious-metal catalysts from acros organics for coupling reactions in organic synthesis ix aromatic nitriles are important pharmaceuticals1 and agrochemicals and are also key-intermediates for the synthesis of carboxylic acids benzyl amines and other important chemicals the substitution of aromatic halides by cyanide is amongst others2 a general route to make aromatic nitriles the well known synthesis via the rosenmund-von-braun-reaction3,4 with stoichiometric amounts of coppericyanide requires unfortunately harsh reaction conditions the catalytical reactions with nickel5,6,7 and palladium,8,9,10,11,12 compounds have recently opened a direct and rapid approach to aromatic nitriles these reactions proceed at relatively mild conditions and have depending on the reaction conditions partly very good yields a limitation is the fact that the catalyst is often deactivated by cyanideions6,13 another limit is the low reactivity of the cheap and easily available

negishi-coupling1,2 precious-metal catalysts from acros organics for coupling reactions in organic synthesis x the negishi-coupling is a widely used nickel3 or palladium-catalysed reaction for the synthesis of unsymmetrical biaryls4 and biaryl-methanes5 from arylzinc halides or benzylic zinc halides alkyl-6,7,8,9,10 alkenyl-11,12 and alkynyl-13 zinc halides can also be used for the coupling as well as wide variety of substrates like aryl alkyl and alkenyl14 halides and -tosylates7 also heterocycles like halogen furans and halogenated thiazoles have been utilized successfully15 due to the mildness stereo and chemo selectivity and high yields the negishi-coupling has been successfully used in the synthesis of complex molecules21 a recent example is the formation of a key intermediate in the total synthesis of discoderminolide22 besides the broad scope of reactants also many functional groups can be present in the molecules16,17,18 because the zinc-organic compounds are much more

n-heterocyclic carbenes as new ligands for cross-coupling and metathesis reactions precious-metal catalysts from acros organics for coupling reactions in organic synthesis xi n-heterocyclic carbenes nhc have emerged as a new class of σ-donor ligands with similar and even superior electronic characteristics as phosphine-ligands1 the nhc’s a and b can be easily prepared from the corresponding imidazolium-ions and imidazolidinium ions with base2,3,4,5 in the presence of a suitable metal the nhc form complexes6 which are very useful as catalysts for cross-coupling reactions7 i.e with palladium or methatesis-8,9,10 reactions with ruthenium compared with phosphine ligands the nhc-metal complexes have a very high catalytical activity combined with a improved stability and endurance of the catalyst under reaction conditions7 some examples for n-heterocyclic carbenes and carbene-precursors from acros organics 1,3,4-triphenyl-4,5-dihydro-1h-1,2,4-triazol-5-ylidene 36394